1. Field of the Invention
The present invention relates to variable force shakers and more particularly relates to a tree shaker having a fixed weight and an adjustable weight, which adjustable weight may be moved accurately between a balanced position diametrically opposed to the fixed weight which results in no shaking when rotated; and a plurality of unbalanced positions which provides variable shaking forces of a plurality of desired magnitudes.
1. Description of the Prior Art
Mobile tree shakers for harvesting fruit or nuts (produce) from trees are well known in the art. Assignee's U.S. Pat. No. 4,194,347 to Peters discloses a conventional mobile tree shaker; and U.S. Pat. No. 3,964,244 to Vallicello discloses a mobile tree shaker having wings for collecting the fruit or nuts shaken from the trees.
The above conventional tree shakers include a shaking assembly which is clamped to the trunk or limbs of a tree for shaking fruit or nuts therefrom. The above prior art shakers include two imbalanced, non-adjustable counterrotating counterweights which are rigidly secured to shafts which apply shaking forces to either the trunk or limbs of a tree as soon as the shafts start to rotate and continue to shake the tree until rotation is stopped. The tree shaker system has a low natural frequency which results in large excursions or amplitudes of shake at the start and end of each shake. These excursions are potentially damaging both to the bark and to the tree system. By having the shaker heads in balance while passing through these frequencies, the problem can be avoided.
Furthermore, it is possible to harvest with the shaker heads rotating continuously, which will save time and fuel. Additional benefits will also be gained when harvesting soft fruit.
When harvesting soft fruit with the prior art fixed eccentricity tree shakers, the fruit is typically detached in several short violent bursts. During the start and at the end of each burst, high amplitude excursions occur, which result in substantial damage to undetached fruit which hit limbs or other undetached fruit. Also, if one-third to one-half of the total crop is detached in a period of one or two seconds due to the violent burst, considerable damage results from fruit landing on other fruit in well known catch frames.
This design would also lend itself to on-board computer control, where pre-established shaking patterns and frequencies could be used, or feed-back sensors to optimize the individual shake would be used.